In Thalassemia, both increased iron alimentary absorption and repeated transfusions can cause iron overload. These iron deposits may occur in many organs and tissues in the body with deleterious effects on the patients health. In the research leading to improved clinical management of Thalassemia major, methods of reducing iron burdens by chelation therapy are being investigated. These studies have been hampered by the lack of sensitive quantitative measure of body stores of iron. The following proposal offers a unique quantitative, non-invasive measure of iron deposits to be applied in the above chelation therapy programs in order to evaluate quantitatively their effectiveness. The quantification of body stores of iron rests on a newly developed technique of nuclear resonance scattering. In this technique, the nucleus of 56Fe (92% isotopic abundance) is raised to its first excited state by gamma radiation. The excited nucleus decays to ground state by emission of the 847 KeV gamma-ray. This gamma ray is measured by special detection instrumentation. During the initial three years the patient irradiation facility was continually improved in sensitivity. The prototype facility which was built from separate bricks and tungsten bars, was replaced by a stainless steel rectangular container designed specially to accommodate exchangeable collimators and disposable furnaces. The iron content of the liver and heart of 28 Thalassemic patients and 4 patients with hemochromatosis iron overloads have been measured, to date. In the next phase, this facility will be used to measure changes in iron deposits in Thalassemic patients and patients with hemosiderosis and hemochromatosis currently undergoing chelation therapy. The specific question to be answered is whether the current chelation therapy effectively stabilizes or reduces iron stores in the heart and liver of transfusion dependent iron overloaded patients.